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CVE Record

CVE-2025-21639: sctp: sysctl: rto_min/max: avoid using current->nsproxy

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: rto_min/max: avoid using current->nsproxy As mentioned in a previous commit of this series, using the 'net' structure via 'current' is not recommended for different reasons: - Inconsistency: getting info from the reader's/writer's netns vs only from the opener's netns. - current->nsproxy can be NULL in some cases, resulting in an 'Oops' (null-ptr-deref), e.g. when the current task is exiting, as spotted by syzbot [1] using acct(2). The 'net' structure can be obtained from the table->data using container_of(). Note that table->data could also be used directly, as this is the only member needed from the 'net' structure, but that would increase the size of this fix, to use '*data' everywhere 'net->sctp.rto_min/max' is used.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Linux kernel flaw can let a local authenticated user trigger a kernel crash, causing denial of service. It is not described as a remote code execution or data theft issue. Business urgency is highest where shared Linux hosts, appliances, or systems with untrusted local users rely on affected kernels.

Executive priority

Treat as a routine but real availability risk. It should enter normal kernel patch cycles, with faster handling for shared infrastructure, regulated appliances, or systems where local user access is not tightly controlled.

Technical view

CVE-2025-21639 is a CWE-476 null pointer dereference in Linux SCTP sysctl handling for rto_min/rto_max. The vulnerable code used current->nsproxy to find the network namespace, which can be NULL while a task exits, causing an Oops. The fix obtains the net structure from table->data instead.

Likely exposure

Exposure is local. Systems running affected Linux kernel versions are relevant, especially multi-user servers, container hosts, and vendor appliances using affected kernels. The bundle references Linux stable fixes plus Debian LTS and Siemens advisories, so downstream package and product impact should be checked there.

Exploitation context

The source bundle lists CVSS 5.5 with local access, low complexity, low privileges, no user interaction, and high availability impact. It states syzbot observed the crash using acct(2). KEV is false, and the bundle provides no evidence of active exploitation.

Researcher notes

The vulnerability is caused by namespace lookup through current->nsproxy in SCTP sysctl rto_min/rto_max paths. The source says table->data can provide the net structure and avoids NULL current->nsproxy cases. Evidence supports denial of service only; no confidentiality or integrity impact is cited.

Mitigation direction

  • Update affected Linux kernels using vendor-provided fixed packages or stable branch fixes.
  • Check Debian LTS and Siemens advisories if those products or distributions are in scope.
  • Prioritize shared hosts and systems with untrusted local users.
  • Where immediate patching is delayed, limit local account access to trusted users.
  • Track vendor guidance rather than applying unvalidated kernel changes.

Validation and detection

  • Inventory Linux kernel versions across servers, containers hosts, and appliances.
  • Compare running kernels against vendor advisories and referenced stable fixes.
  • Confirm SCTP kernel support and related sysctl exposure where relevant.
  • Verify patched hosts no longer report vulnerable kernel builds.
  • Review local-user exposure on systems awaiting updates.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-476: Exact CWE lookup

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cve · low confidence lookup

CVE-2025-21639 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
3ADP providers
11Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2025-21639Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5, 4f3fdf3bc59cafd14c3bc2c2369efad34c7aa8b5unaffected
LinuxLinux3.13, 0, 5.4.290, 5.10.234, 5.15.177, 6.1.125, 6.6.72, 6.12.10, 6.13affected
Weakness

CWE details

CWE-476

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.